Records
Substantiation
The evidence that a claimed deduction actually happened and was for business.
A deduction is not the charge on the statement. It is the charge plus enough record to show what it was for, and the standard varies by kind of expense.
Receipts are generally required for lodging and for expenses of $75 or more; below that a record of the amount, date, place and business purpose is expected but a paper receipt is not. Travel, meals and vehicle use carry their own rules.
The burden is on the taxpayer. An expense with no record behind it is not a disputed deduction, it is an absent one.
In Contha
Contha states the $75 line on the worksheet and says how much of what you have claimed is over it with nothing attached.